The present invention relates to a drive device for a motor vehicle and to a method of operating such a drive device.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
A drive device is used to propel a motor vehicle, i.e. to provide a torque for propelling the motor vehicle. The drive device includes a secondary air device to provide secondary air for injection into an exhaust pipe. The exhaust pipe carries away exhaust generated by the drive device, in particular an internal combustion engine of the drive device. Secondary air involves fresh air, i.e. air, drawn from the ambient environment and injected chemically unaltered into the exhaust pipe. Injection of secondary air into the exhaust increases the oxygen content of exhaust to thereby enable oxidation of possibly unburned fuel in the exhaust. As a result, unburned fuel is prevented from being released together with exhaust into the environment.
A secondary air path is provided to supply secondary air to the exhaust pipe. Secondary air flows along the secondary air path when need be. The secondary air path normally extends from an intake device, by which air is drawn from the outside environment of the drive device, to the exhaust pipe. The intake device, by which secondary air reaches the secondary air path, can include an air filter. A secondary air pump to convey secondary air in the direction of the exhaust pipe and a secondary air valve are provided in the secondary air path, with the secondary air valve selectively closing or, at least partially, in particular fully, opening the secondary air path. The secondary air valve has two switching states. In one state, the secondary air path is fully closed by the secondary air valve, and in the other state, the secondary air path is completely open. The secondary air valve is also provided to adjust a particular secondary air mass flow rate through the secondary air path.
The secondary air mass flow rate along the secondary air path depends on the secondary air pump which is normally electrically operated. When the supply voltage of the secondary air pump changes, e.g. as a result of unavoidable voltage fluctuations of an on-board electrical system of the motor vehicle, the secondary air mass flow can deviate from a predefined desired mass flow.
It would therefore be desirable and advantageous to provide an improved drive device for a motor vehicle to obviate prior art shortcomings and to realize a constant secondary air mass flow within a broad operating range for supply of secondary air to the exhaust pipe.